1. Field of the Invention
The present invention relates to a light emitting diode lamp and a method for producing the same.
2. Description of the Related Art
Traditionally, many light emitting diode (hereinafter referred to as LED) lamps are manufactured by casting method which utilizes a casting mold. To form an LED lamp by casting method, the heads of lead terminals, one of which holds a light emitting element, are dipped into an epoxy resin which fills a cast. After curing of the epoxy resin, the lead terminals and their heads are encapsulated by the epoxy resin.
FIG. 9 is a side view of a conventional LED lamp, and FIG. 10 is a side view of the LED lamp of FIG. 9 as mounted on a substrate. In this case, when lead terminals 82 are dipped into an epoxy resin, surface tension at the resin surface causes the epoxy resin to creep up the basal portions of the lead terminals 82 which stick out of the bottom surface of a light emitting body 81. Inevitably, as illustrated in FIG. 9, the finished LED lamp 8 has resin bumps 84 around the basal portions of the lead terminals 82 which stick out of the bottom surface of the light emitting body 81.
Currently, with automation of the LED mounting operation, an LED lamp is directly mounted on a substrate in many cases. When leads are clinched during the automatic mounting process, the LED lamp is pulled by a lead clinching force and pressed against the substrate. In this situation, as shown in FIG. 10, the resin bumps 84 around the basal portions of the lead terminals 82 cut into, and eventually block, the terminal holes 86 in the substrate 85. In another respect, a gas is trapped in a space between the lead terminals 82 and the terminal holes 86. Under the soldering heat, the gas expands so much as to burst out toward the solder 87 side, leaving a lot of blow holes (not shown) in the solder 87. Hence, the conventional technique severely loses reliability in mounting the LED lamp 8 on the substrate. As a further disadvantage, if blow holes are found, a worker has to mend the area manually after the soldering step. Thus, generation of blow holes costs additional labor.
A technique for solving this problem is disclosed, for example, in Japanese Patent Laid-open Publication No. H5-243620. With respect to an LED lamp 9 illustrated in FIG. 11, a light emitting body 91 has a notch 93 which is formed along a part of the bottom periphery. The notch 93 serves to vent a gas trapped in a space between the surface of a substrate 95 and the light emitting body 91, thereby preventing generation of blow holes in soldering areas 97.
Nevertheless, unlike the condition illustrated in FIG. 11, the outer diameter of lead terminals 92 including the resin bumps 94 may be out of proportion relative to the inner diameter of terminal holes 96 in the substrate 95. Namely, because the conventional LED lamp 9 has the resin bumps 94 formed around the basal portions of the lead terminals 92, the outer diameter of the lead terminals 92 may possibly become larger than the inner diameter of the terminal holes 96. Under such circumstances, when the light emitting body is pulled against the substrate by a lead clinching force, the resin bumps block the terminal holes. After all, this technique may fail to vent a gas which is trapped in the space between the lead terminals and the terminal holes, thus leaving the possibility that blow holes may generate in soldering areas.
In view of these problems, it is an object of the present invention to provide a more reliable LED lamp with a reduced probability of occurrence of defective LED lamps, by surely preventing generation of blow holes in soldering areas of the LED lamp, and also to provide a method for producing such an LED lamp.
In order to achieve this object, the light emitting diode lamp of the present invention comprises a pair of lead frames, a light emitting element mounted on a head of one of the lead frames, and a light emitting body which encapsulates heads of the lead frames and the light emitting element by resin molding, with the pair of lead frames having legs which stick out of a bottom surface of the light emitting body, wherein the light emitting body is provided with a protrusion at an appropriate position along the periphery of the bottom surface, the protrusion projecting away from the light emitting body, beyond an area in the bottom surface where the legs of the lead frames stick out.
FIG. 6(a) is a bottom view of an LED lamp whose lead frames are positioned at the center, and FIG. 6(b) is a bottom view of an LED lamp whose lead frames are offset from the center.
With respect to the LED lamp 30 shown in FIG. 6(a), the distances from the lead frames 16 to any two points on the circumference of the LED lamp 30 are equal (A=B in the illustration). In this situation, due to surface tension, a resin which creeps up the lead frames 16 develops proportionate bumps (A=B in the illustration).
In contrast, with respect to the LED lamp 40 shown in FIG. 6(b), the distances from the lead frames 16 to two points on the circumference of the LED lamp 40 are different (A greater than B in the illustration). In this situation, due to surface tension, a resin which creeps up the lead frames 16 develops disproportionate bumps (A less than B in the illustration).
According to the above LED lamp of the present invention, even in the case where the light emitting body which has bumps of molding resin around the legs of the lead frames is directly mounted on a substrate, it is possible to secure a clearance between the bottom surface of the light emitting body and the substrate. Besides, when the light emitting diode lamp is pulled toward the substrate by a lead clinching force, the resin bumps around the legs of the lead frames do not block holes formed in the substrate for the lead frames.
Regarding this LED lamp, the protrusion may be provided at a farthest position from the lead frames.
In this case, when the resin is influenced by surface tension, most of the resin creeps up the protrusion provided at a farthest position from the lead frames. Hence, the resin is efficiently deterred from creeping up in the B direction of FIG. 6(b). Consequently, in the case where the light emitting body is directly mounted on the substrate, it is possible to mount the light emitting body on the substrate surface in a more stable manner.
Further regarding the LED lamp, the light emitting body may be provided with two such protrusions at two positions along the periphery.
With this arrangement, the light emitting body can be stably mounted on the substrate. Besides, formation of the protrusions can be rationalized.
A method of the present invention for producing a light emitting diode lamp comprises forming a light emitting body by casting method, with the use of a mold which has a protrusion forming part at an appropriate position along a top periphery of the mold.
This method enables easy production of the light emitting diode lamp which has the above-mentioned protrusion.
Thus, the above method can omit a laborious blow hole treatment which is conventionally performed after the LED lamp is mounted on the substrate. As a result, this method can reduce the production time and improve production efficiency. Further, this method can decrease the probability of occurrence of defective LED lamps, so that LED lamps can be produced with higher reliability.
Notably, the production of the above LED lamps does not require any new equipment. Since the LED lamp production can be embodied simply with the use of a mold having a protrusion forming part concerning the present invention, it is possible to manufacture LED lamps without a significant economic burden.